The invention relates to a system for automatically and simultaneously loading a plurality of boat loads of semiconductor wafers into a semiconductor diffusion furnace.
Commonly assigned U.S. Pat. No. 5,765,982 by Martin et al., issued Jun. 16, 1998 is incorporated by reference herein, and is believed to be representative of the closest prior art. FIG. 1A of U.S. Pat. No. 5,765,982 shows a furnace loading station 10. A queue mechanism 30 having a stationary base is loaded with 6 to 8 boatloads of semiconductor wafers 26. The queue mechanism 30 shifts the right hand boatload of wafers to an index position at the right end of queue mechanism 30 such that a pair of horizontal elevator tines 38 of a vertical elevator mechanism 34 can pick up one boatload of wafers at a time in the manner of a fork lift, raise them upward in the direction of arrows 60 into alignment with one of a number of horizontal loading assemblies such as 14 and 16. Each loading assembly includes a carriage such as 20 or 42 which moves horizontally on a track toward a semiconductor furnace tube located in a furnace cabinet on the right hand side of furnace loading station 10 so that 6 to 8 boatloads of wafers supported on either a horizontal cantilever paddle such as 47 or in a horizontal cantilever diffusion tube such as 21 can be inserted into the hot zone of a corresponding furnace tube.
A horizontal robotic mechanism 37 is supported by vertical elevator 34. Horizontal robotic mechanism 37 supports the tines 38 which pick up one boatload of wafers and moves them horizontally in the direction of arrows 39 to position each boatload of wafers, one at a time, over the paddle 47, lower it onto the paddle 47. After 6 to 8 boatloads of wafers have been loaded onto cantilever paddle 47, the carriage 42 supporting the paddle 47 moves in the direction of arrow 59 into the hot zone of the corresponding furnace tube. The entire operation is controlled by a programmed computer or control system 29 that controls the various described moving mechanisms.
A major shortcoming of the foregoing system of U.S. Pat. No. 5,765,982 is that the process of loading and unloading each cantilever paddle 47 with 6 to 8 boatloads of wafers one at a time, inserting them all at once into and withdrawing them all at once from the furnace tube, the unloading of the processed boatloads of wafers one at a time and depositing them back on the queue mechanism 30 is very time-consuming. A typical prior art loading station 10 includes four loading assemblies such as 16, so 24 to 32 boatloads of wafers have to be transferred one at a time from queue mechanism 30 and loaded one at a time onto the cantilever paddles 47 prior to processing them in the furnace tube. After processing they then must be unloaded from paddles 47 one at a time and returned to queue mechanism 30. This may require a total of more than 15 minutes. The mechanism 30 in U.S. Pat. No. 5,765,982 is undesirably complex and slow.
Other prior art exists which provides an intermediate carrier that can support 6 to 8 boatloads of wafers and load all 6 to 8 boatloads in a single pass onto a cantilever paddle such as 47 in U.S. Pat. No. 5,765,982. Most such prior art systems use complex 5-axis articulated mechanisms to support the intermediate carrier and the 6 to 8 boatloads of wafers on it. Both the hardware and software of these systems are more complex and expensive than is desirable.
Accordingly, it is an object of the invention to provide an automatic wafer boat loading system which reduces the amount of time required to load a plurality of boatloads of semiconductor wafers into a semiconductor diffusion furnace and to later unload them from the furnace.
It is another object of the invention to provide an automatic wafer boat loading system which avoids the need for separate operations to load a plurality of wafer boats, one at a time, onto a cantilever paddle.
It is another object of the invention to provide an automatic wafer boat loading system which avoids generation of particulates due to abrasion that results from imprecise placement of loader wafer boats on a cantilever paddle.
It is another object of the invention to provide an automatic wafer boat loading system which reduces the number of loading and unloading cycles required to load a plurality of boatloads of wafers into a diffusion furnace and later unload them from the furnace.
It is another object of the invention to provide an automatic wafer boat loading system which is operable using relatively simple software.
It is another object of the invention to provide a system for simultaneously loading a plurality of boatloads of wafers into a furnace tube without introducing an excessive amount of additional thermal mass and physical mass into the furnace tube in order to avoid disturbing semiconductor process parameters within the furnace tube.
Briefly described, and in accordance with one embodiment thereof, the invention provides an apparatus for automatically and simultaneously loading a xe2x80x9clongxe2x80x9d wafer boat or a plurality of wafer boats onto a cantilever paddle, and automatically and/or simultaneously unloading the loaded wafer boats from the cantilever paddle. The apparatus includes a stationary first track aligned with a first opening of a furnace, and a first carriage moveable on the first track, the first carriage supporting a first cantilever paddle. A first vertical translation mechanism includes a first stationary part and a first vertically moveable support. A second vertical translation mechanism includes a second stationary part and a second vertically moveable support. A first horizontal translation mechanism includes a first base supported by the first vertically moveable support and a first horizontally moveable arm supported by the first base. A second horizontal translation mechanism includes a second base supported by the second vertically moveable support and a second horizontally moveable arm supported by the second base. A horizontal support apparatus is adapted to support the wafer boat or boats each loaded with semiconductor wafers. The support apparatus includes a first end supported by the first horizontally moveable arm and a second end supported by the second horizontally moveable arm.
In one embodiment, the horizontal support apparatus includes a first wafer boat edge lift mechanism having a first end supported by the first horizontal arm mechanism and a second end supported by the second horizontal arm mechanism. The first wafer boat edge mechanism includes at least a first retractable boat edge engaging member. The horizontal support apparatus also includes a second wafer boat edge lift member having a first end supported by the first horizontal arm mechanism and a second end supported by the second horizontal arm mechanism. The second wafer boat edge lift member includes at least a second retractable boat edge lift member. The first and second retractable edge engaging members are extendable to engage opposite edges of the loaded wafer boat or boats to support and set boat or boats directly on the cantilever paddle by movement of the first and second horizontal arm mechanisms in the first and second vertical translation mechanisms. The first and second retractable boat edge engaging members are retractable to allow withdrawal of the first and second horizontal arm mechanisms from the vicinity of the loaded wafer boat or boats on the cantilever paddle.
In another embodiment, the horizontal support apparatus includes an intermediate carrier having first and second ends removably supported by the first and second horizontally moveable arms, respectively. The plurality of loaded wafer boats rests on the intermediate carrier, the intermediate carrier with the plurality of wafer boats thereon being adapted to be gently set on the cantilever paddle by movement of the first and second horizontal arm mechanisms in cooperation with movement of the first and second vertical translation mechanisms. In another embodiment, a single long wafer boat includes end features by which the long wafer boat is directly supported by the first and second horizontal arm mechanisms, without use of an intermediate carrier.